1. Field of the Invention
The present invention relates to an apparatus and method for treating semiconductor substrates and, more particularly, to an apparatus and method for chemically mechanically polishing and cleaning semiconductor substrates.
2. Description of Related Art
A process for manufacturing semiconductor devices comprises a deposition process for forming a thin film on a wafer and an etch process for forming a fine circuit pattern on the thin film. These processes are iteratively performed until a desired circuit pattern is formed on the wafer. In this case, many curvatures are produced. With the recent trend toward finer semiconductor devices, the line widths of circuits are smaller and more interconnections are stacked on a chip. For this reason, a step difference based on inner positions of the chip increases. The step difference makes it hard to uniformly coat a conductive layer in a subsequent process and causes a defocusing in a photolithographic process.
In view of the foregoing, there exist many ways for planarizing a wafer surface. As wafer calibers become larger, chemical mechanical polishing (CMP) has been widely used in recent years because a superior planarity can be achieved at not only a narrow area, but also wide area.
Typically, there are two methods for polishing wafers up to a target thickness during a CMP process. One is a time method, and the other is an endpoint detecting method. In the time method, a user sets the polishing time according to the thickness, and kinds of layers and wafers are polished for this set time. Unfortunately, the time method cannot polish wafers to an exact thickness due to the abrasion state of expendable supplies such as polishing pads or polishing conditioners used in a polishing process, the pressure of the polishing head for pressurizing wafers during the polishing process, hunting in the amount of slurries supplied, and the various states of layers.
The endpoint detecting method is classified further into a motor current detecting method and an optical detecting method. The motor current detecting method is a method for detecting the variation of a load applied to a motor resulting from a frictional force of two different layers. The motor current detecting method is advantageous in the cases where a polishing point is a boundary of an upper layer and a lower layer, but the method cannot be used in the case where a polishing point is the specific point of a single layer. The optical detecting method is a method using an intrinsic reflectivity of a material. Specifically, the optical detecting method uses a combination of waveforms reflected at a surface of a layer and at a boundary face of layers from a scanned regular wavelength beam. The optical detecting method is advantageous in the case where an upper point or a lower point is clear-cut, but this method cannot be used in the case that the upper or lower point is not clear-cut or the desired thickness is small. It is therefore hard to polish wafers to an exact thickness with currently used polishing methods.
Generally, a cleaning apparatus is disposed at one side of a polishing apparatus to remove extra substances such as slurries remaining on a wafer after a polishing process is performed. A typical cleaning apparatus has a cleaning module, a plurality of etchant treating modules, and a drying module. A completely polished wafer is cleaned using deionized water (DI water) from the cleaning module. The wafer is then rinsed at a module using a mixed chemical containing ammonia, hydrogen peroxide, and DI water. After being cleaned by a brush at a module using hydrofluoric acid (HF) as a chemical, the wafer is dried by a spin driver in the drying module. In the case that the cleaning process is performed using the above-described procedure, slurry residues and particles of the brush may remain attached to the wafer. Afterwards, the wafer is transferred to a wet station to be rinsed using the mixed chemical and is dried using isopropyl alcohol (IPA) based on Marangoni effect. Thus, duplicate time is required for cleaning wafers due to the slurry residues and the particles of the brush. In the respective modules of the cleaning apparatus, wet wafers are transferred to the modules by means of a transfer unit. Accordingly, the chemical may drop on the modules thereby staining or contaminating the modules.